# Dark-Matter-Enhanced Probe of Relic Neutrino Clustering

## TL;DR

This paper explores how decaying heavy dark matter can produce ultrahigh-energy neutrinos, which, through their interactions with the cosmic neutrino background, can reveal properties of relic neutrino clustering with future neutrino telescopes.

## Contribution

It introduces a novel method using heavy decaying dark matter as a probe for relic neutrino background and clustering effects via ultrahigh-energy neutrino observations.

## Key findings

- Local CνB overdensity of >10^6 can be detected at IceCube-Gen2 within ten years.
- Neutrino interactions with CνB can provide insights into neutrino mass and dark matter properties.
- Complete neutrino transport modeling enhances the accuracy of flux predictions.

## Abstract

We propose heavy decaying dark matter (DM) as a new probe of the cosmic neutrino background (C$\nu$B). Heavy DM, with mass $\gtrsim 10^9$ GeV, decaying into neutrinos can be a new source of ultrahigh-energy (UHE) neutrinos. Including this contribution along with the measured astrophysical and predicted cosmogenic neutrino fluxes, we study the scattering of UHE neutrinos with the C$\nu$B via standard weak interactions mediated by the $Z$ boson. We solve the complete neutrino transport equation, taking into account both absorption and reinjection effects, to calculate the expected spectrum of UHE neutrino flux at future neutrino telescopes, such as the IceCube-Gen2 radio. We argue that such observations can be used to probe the C$\nu$B properties and, in particular, local C$\nu$B clustering. We find that, depending on the absolute neutrino mass and the DM mass and lifetime, a local C$\nu$B overdensity $\gtrsim 10^6$ can be probed at the IceCube-Gen2 radio within ten years of data taking.